The stretch between 4th and 6th was once the scene of homeless encampments. Today, boutiques and cafes cater to new residents. The catalyst was the adaptive reuse ordinance, launched 10 years ago.

A decade ago, the stretch of downtown L.A.'s Main Street between 4th and 6th streets was a desolate collection of empty buildings and homeless encampments, an area where drug dealing was conducted in the open, and the only longtime residents lived in residential hotels. These days, that stretch resembles a bustling small-town main street.

There's the neighborhood bookstore, where an attentive shopkeeper knows her customers by name. A DVD store that stocks the kind of films that appeal to the hip residents who live in the building upstairs. And shop owners and customers who live side by side above the stores.

While much of downtown is struggling to attract the kind of ground-floor retail that many urbanists say is essential to turning a cluster of residential units into something more like a neighborhood, downtown's historic core has been seeing a surge forward lately.

Some downtown boosters who track such developments say that the vast majority of retail space along Main Street, from 4th to 7th Street, is now leased -- an accomplishment that they are touting as a sign of the neighborhood's successful reinvention.

The changes along Main Street -- and in downtown's historic core in general -- were launched 10 years ago this month, when a new city ordinance went into effect that made it easier to convert former bank, office and industrial buildings into residential and small retail spaces.

The ordinance was little noticed at the time. But the adaptive reuse ordinance, as it is known, has profoundly changed the way the city thinks about its long-neglected urban center. It streamlined the city's permitting process for those seeking to re-purpose the old buildings and allowed for flexibility in the city's zoning and code requirements.

"After decades of beating a dead horse, they realized that commercial was not going to come back to this neighborhood the way it was," said Bert Green, owner of an art gallery at 5th and Main. "It made sense to change the use of the buildings."

In 1999, downtown Los Angeles was an area very much in transition. The Staples Center had just opened. Walt Disney Concert Hall, L.A. Live and other downtown attractions were still years away from opening. Only 18,000 people lived in the city center.

"We had offices, we had some cultural attractions," said Carol Schatz, president and chief executive of the Central City Assn., a business advocacy group that pushed for the change. "But the one thing that we knew we needed to make downtown survive and thrive was residents."

While bigger, more extravagant projects for downtown were announced, and some even got underway, Historic Downtown kept plugging away.

"It may have been constructed," said developer Tom Gilmore, who many credit as the architect of the historic core's reinvention, "but it's not contrived."

Apartments and lofts in buildings were rented; some condos sold and retail spaces slowly began to fill along both Main and Spring streets. An art walk highlighted the assortment of galleries in the area. Restaurants began to draw people from beyond downtown.

"The community was organically grown by seeing what was needed and what could survive as destination retail," said Brady Westwater, a local activist and the former president of the Downtown L.A. Neighborhood Council, who has been instrumental in bringing businesses to the area.

Still, life in Historic Downtown is not for everyone. The area, just a few blocks away from Skid Row, continues to be a magnet for the homeless. It is still gritty and lacks the sort of luxurious high rises as other parts of the city center.

But even as other parts of downtown have seen some large-scale projects canceled and other condo developments switch to rentals as a way to ride out the economic storm, Historic Downtown has continued to collect new businesses: clothing stores, restaurants, bars and other amenities. Two new affordable housing projects are being developed.

Residents and shop owners in the area say that the relatively low cost of space in the area, combined with a certain amount of flexibility, has allowed them to take a chance in the area.

Jose Caballer, who lives in Gilmore's San Fernando building and runs a digital design firm out of an old bank building a few doors to the west, said that part of the appeal of the area is that it's like a sort of undiscovered country. "You can go and look at buildings and say, I want to do events here. If you are creative and resourceful enough . . . you can do it."

Brittany Hoa Pham, owner of Fremont clothing, said that her location along 4th Street has meant that, "We get an interesting group of people." But she admits that "once in a while, a homeless man or woman comes in and frightens me."

The challenge now for Historic Downtown, said Gilmore, is "how we end up a sustainable neighborhood, not a flash in the pan."

That's something that has been taking up a lot of Westwater's time recently.

After seeing success along Main and Spring streets, he has turned his attention to Broadway, where recent community efforts have focused on finding new uses for a collection of old movie houses and retail and office space along the street.

"We showed we could fix Main Street," he said. "Now, the challenge of developing a Broadway that works for everyone is the next step."